This invention relates to friction welding and, more specifically, to the joining of structural members by friction plug welding.
Structural assemblies, such as those in the aerospace industry, are often constructed by joining structural members together. The structural members can be joined to one another by welding along the joint interface between the members or using fasteners, such as rivets, screws, or bolts. Oftentimes it is necessary to join structural members that have complex geometries or configurations that complicate the joining process. For example, when joining structural members having curvilinear configurations, it can be difficult to position and secure the members relative to one another while preventing gapping and maintaining the joint interface free of obstruction. Similarly, some structural members have configurations that restrict access to the joint interface between the members. For example, when joining a dome to a cylinder to form a tank or the exterior of an aerospace vehicle, such as a rocket or missile, it can be difficult to simultaneously support and secure both the inside and outside of the dome and cylinder.
Conventionally, when joining structural members having complex configurations and/or joint interfaces that are difficult to access, a built-up structure or tooling is constructed between the structural members to assist in positioning and securing the structural members while they are joined. For example, when joining a dome to a cylinder, one or more backing plates or other support members (xe2x80x9ctoolingxe2x80x9d) can be added to the cylinder and dome to facilitate positioning the dome on the cylinder and to support the joint interface between the structural members as they are joined. The tooling can then be removed after the structural members are joined. However, constructing the tooling requires labor, time, and materials, thus increasing the manufacturing cost of the structural assembly. Similarly, the removal of the tooling requires additional labor and machining time, which further increases the manufacturing cost. In some cases, it can be difficult or impossible to access and remove the tooling after the structural members have been joined, which can adversely affect the overall weight of the resulting structural assembly. Weight and strength are of critical concern in the aerospace industry.
In seeking to reduce manufacturing costs, other methods of joining structural members having complex configurations have been proposed. One such method involves using fasteners, such as rivets, to join the structural members together. However, because rivets generally require pre-drilled holes, joining structural members using rivets can be labor intensive and time consuming. In addition, the types of joint configurations that can be joined using rivets are limited since rivets require that the structural members overlap at the joint interface or a support member or backing plate overlaps each of the structural members. Rivets can also interfere with the process of forming a secondary weld joint along the joint interface between the structural members. More specifically, the rivets may not be entirely consumed in the weld joint, which can result in stress concentrations in the finished structural assembly that can reduce the fatigue strength of the assembly.
Thus, there remains a need for an improved method of joining structural. members to form structural assemblies. The method should be cost effective and should facilitate the joining of structural members having a variety of configurations, including structural members having complex configurations or joint interfaces that are difficult to access. The method should be effective regardless of whether the structural members overlap. Additionally, the method should be compatible with other joining methods, such as fusion welding techniques and friction stir welding methods.
The present invention provides a method for manufacturing a structural assembly. According to one embodiment of the present invention, the method includes the steps of positioning a first structural member at least partially adjacent a second structural member to define an interface therebetween. A rotating plug is then inserted into the first and second structural members at the interface to thereby join the first structural member to the second structural member. In one embodiment, the method of manufacturing includes drilling an aperture in at least one of the first and second structural members. The aperture is structured to receive the plug. In another embodiment, the plug is machined to predetermined dimensions before it is inserted into the first and second structural members. In another embodiment, at least one end of the plug is machined subsequent to inserting the plug so that the end of the plug is flush with the outer surface of the corresponding structural member. In another embodiment, the method includes forming an elongate weld joint between the first and second structural members along the interface and wherein the elongate weld joint at least partially consumes the plug. For example, according to one embodiment, the elongate weld joint is formed by inserting a rotating friction stir welding probe into the first and second structural members at the interface and moving the rotating friction stir welding probe through the first and second structural members along a path defined by the interface. In yet another embodiment, the method includes repeating the inserting step at positions along the interface. For example, according to one embodiment, a rotating plug is inserted at a position at least partially overlapping an existing plug. In still another embodiment, the method includes securing the structural assembly to other structural assemblies to form the frame of an aerospace vehicle.
According to another embodiment of the present invention, the method of manufacturing a structural assembly includes the steps of positioning a first structural member at least partially adjacent a second structural member to define an interface therebetween. A plug is positioned adjacent the outer surface of the first structural member. The plug is rotated, and, concurrently with the rotating step, is inserted into the first and second structural members. In one embodiment, the method of manufacturing includes drilling an aperture in at least one of the first and second structural members. The aperture is structured to receive the plug. In another embodiment, the plug is machined to predetermined dimensions before it is inserted into the first and second structural members. In another embodiment, at least one end of the plug is machined subsequent to inserting the plug so that the end of the plug is flush with the outer surface of the corresponding structural member. In another embodiment, the method includes forming an elongate weld joint between the first and second structural members along the interface and wherein the elongate weld joint at least partially consumes the plug. For example, according to one embodiment, the elongate weld joint is formed by inserting a rotating friction stir welding probe into the first and second structural members at the interface and moving the rotating friction stir welding probe through the first and second structural members along a path defined by the interface. In yet another embodiment, the method includes repeating the inserting step at positions along the interface. For example, according to one embodiment, a rotating plug is inserted at a position at least partially overlapping an existing plug. In still another embodiment, the method includes securing the structural assembly to other structural assemblies to form the frame of an aerospace vehicle.
The present invention also provides a structural assembly comprising a first structural member and a second structural member that is positioned at least partially adjacent to the first structural member so as to define an interface therebetween. At least one friction plug weld joint joins the first structural member to the second structural member. In one embodiment, the friction plug weld joint has a tapered configuration. In another embodiment, the first and second structural members comprise different materials. In another embodiment, the first and second structural members are formed of aluminum, aluminum alloys, titanium, titanium alloys, or steel alloys. In another embodiment, the friction plug weld joint at least partially comprises a material different from the material forming at least one of the first and second structural members. In another embodiment, at least one friction plug weld joint at least partially overlaps another friction plug weld joint. In another embodiment, the friction plug weld joint is perpendicularly disposed in relation to the interface. In yet another embodiment, the friction plug weld joint is angularly disposed in relation to the interface. In still another embodiment, an elongate weld joint joins the first and second structural members. For example, according to one embodiment, the elongate weld joint comprises an arc weld joint, a resistance weld joint, a gas weld joint, or a friction stir weld joint. According to another embodiment, the elongate weld joint at least partially consumes at least one friction plug weld joint
The present invention also provides a structural assembly comprising a first structural member and a second structural member positioned at least partially adjacent to the first structural member so as to define an interface therebetween. At least one friction plug weld joint joins the first structural member to the second structural member and wherein the friction plug weld joint extends through the first structural member at the interface and at least partially into the second structural member. In one embodiment, the friction plug weld joint has a tapered configuration. In another embodiment, the first and second structural members comprise different materials. In another embodiment, the first and second structural members are formed of aluminum, aluminum alloys, titanium, titanium alloys, or steel alloys. In another embodiment, the friction plug weld joint at least partially comprises a material different from the material forming at least one of the first and second structural members. In another embodiment, at least one friction plug weld joint at least partially overlaps another friction plug weld joint. In another embodiment, the friction plug weld joint is perpendicularly disposed in relation to the interface. In yet another embodiment, the friction plug weld joint is angularly disposed in relation to the interface. In still another embodiment, an elongate weld joint joins the first and second structural members. For example, according to one embodiment, the elongate weld joint comprises an arc weld joint, a resistance weld joint, a gas weld joint, or a friction stir weld joint. According to another embodiment, the elongate weld joint at least partially consumes the at least one friction plug weld joint.
Accordingly, there has been provided a structural assembly and an associated method of manufacture allowing for the efficient joining of structural members. The method is cost effective and can be used to join structural members having a variety of configurations, including structural members having complex configurations or joint interfaces that are difficult to access. The method can be used regardless of whether the structural members overlap. Additionally, the method is compatible with other joining methods, such as fusion and friction stir welding techniques.